In order to figure a profit of 10% I would normally take my cost and
then multiply by 1.1 to find the selling price. My employer tells me
that in order to find a 10% profit I should divide my cost by 0.9, but
I don't understand how this is 10%. Can you please explain?

A student struggles to understand the equivalence of 3/5 and 0.6: three clearly goes
into five at least one time; and extending the five into fifty only makes matters worse.
Emphasizing the importance of keeping the dividend and divisor in the right order,
Doctor Peterson clarifies, first explaining fractions with a sharing scenario, then
walking through an example.

Find a nine-digit number such that the first digit is divisible by one,
the first two digits are divisible by 2, the first three digits are
divisible by 3,..., the whole nine-digit number is divisible by nine.

I'm having real problems trying to divide using a non place system,
like with Roman numerals. The concept of using letters rather than
numbers is confusing me. Can you please give me an example of a
division calculation?